Expansive soils (also known as swelling soils or active soils) cause foundation and pavement problems worldwide. Expansive soils are found abundantly in both developed and underdeveloped countries. They are abundant in California, Colorado and Texas. Worldwide, they are found in Oman, South Africa, Palestine, Mexico, China and many other nations. They are a particular problem for lightly loaded structures such as one story houses, pavements, warehouses and airport runways. In the United States, expansive soils cause more loss than fire, flood and earthquake damages combined, each year.
Expansive soils are currently identified by Expansion Index Test, Percent Swell Test, Swelling Consolidation Pressure Test or Potential Vertical Rise Analysis. Clays and claystone materials that contain montmorillonite or illite minerals have been known to swell when they absorb moisture and shrink when moisture is extracted.